and to an extend how do you keep track of which unique part is active in which site if e.g a website gets hacked and resets your current password, because in case of a password manager i just create a new one and be done, on top of my mind i would have the question for you: would you recreate all websites with a new unique part or just create a system for outliers?
not to offend, just had several of these incidents in my years and for me a password manager is much more piece of mind
I think you have a valid point in multi site leaks if the attacker was focused on my account. I will think about it